If you read the update at the bottom, they used an accelerant to actually get ignition to flames. That's pretty crappy that it wasn't disclosed in the original. It's fine that they used it to get those shots, but it's that they didn't disclose that with the original photographs leading us to believe that it was natural combustion.

Update on 7/17/13: Hawaii News Now confirms that this was done as a stunt:

The photo is real, but the flames are not the result of spontaneous combustion. “The flames on the tripod and my shoes did not start because of the lava” Singson freely admits. “It’s like if you put your shoe in a hot frying pan, it will not catch fire right away”.

Singson used an accelerant to start the flames then had his buddy snap the shot. The reason? “It’s just something I wanted for my Facebook cover photo”.